Information management systems (IMS) such as digital library servers typically use a relational database management system (RDBMS) to manage data records in a database. As an example, an IMS might manage document data, with the desire that the RDBMS maintain so-called “referential integrity” for elements in the database. What is meant by “referential integrity” is that if a row of a table (referred to as a “target” table) that is referenced by a row in another table (referred to as a “source” table) by means of a foreign key (referred to as a “pointer”) is sought to be deleted or changed, either the deletion or change is disallowed or the pointer is removed from the source table, so that no “dangling pointers” (i.e., links to nonexistent database elements) remain.
This is but one example of what is meant by “referential integrity”. In general, when one entity refers to another, a dependency relationship is created that represents a referential constraint the integrity of which might be desirable to maintain. As recognized herein, not all such constraints need have their integrity maintained; rather, deciding which constraints to maintain is a balance between application requirements and what can be maintained efficiently.
In existing RDBMS systems such as the system known as “DB2” and marketed by the present assignee, maintaining referential integrity assumes homogenous linking, i.e., that all links from a column of a source table point to tuples in a single predetermined target table. As recognized herein, however, in some cases, such as, for example, digital libraries, a column of links can exist in a table that do not all point to a single common target table. This is because different data types can exist in these cases, so that, for example, one link in a column of a source table might point to a target table representing a particular type of document, another link in the column might point to a target table representing another particular type of document, while yet a third link might point to an image, all of them nonetheless being interrelated. Such links are referred to as “heterogeneously scoped” links, whereby the scope (or target) of these links consists of multiple pre-determined tables. A special case is “unscoped” links, whereby the target tuple of a link can be in any table.
Accordingly, “heterogenous scoping” refers to the ability to create and manage a column of links whose targets are not restricted to being tuples of a single table. It will readily be appreciated by the skilled artisan that heterogenous scoping would provide a flexible and generic linking ability that can be exploited by, e.g., a digital library system to support a relatively more complex data model.
One way to provide heterogenous linking referential integrity is to modify the RDBMS. This is not a trivial task. Accordingly, the present invention is directed to a system and method for providing heterogenous linking referential integrity without modifying the RDBMS, but rather by providing a transparent software layer within the IMS or between the RDBMS and IMS that exploits existing RDBMS functionality to extend referential integrity to heterogeneously scoped links.